I copied the whole downloaded folder to /System/Library/CoreServices/loginwindow.app/Contents/Resources/English.lproj/

When I click at Apple/About this mac the screen goes blank and after some seconds my desktop returns ... but I don't get any popup window from About This Mac.

After the folder copy I changed the owner of AboutThisMac folder.

sudo chown -R root:wheel AboutThisMac.nib

Could that be the problem ?